Some semiconductor wafer processing chambers are of a type in which a magnetic field is produced within the reaction chamber by providing a plurality of electromagnets around the reaction chamber to accelerate formation of the plasma. These chambers use magnetic fields to manipulate plasma density through electron cyclotron rotation.
However, the inventors have observed that the intensity of the magnetic field tends to be greater on the edge of a substrate placed in the reaction chamber than in the center of the wafer. Therefore, when this method of producing a magnetic field is applied to a plasma etching chamber, there is a problem that the etch rate and the selectivity are not uniform over the substrate surface. When the method is applied to a chemical vapor deposition (CVD) chamber, there is a problem of non-uniformity in the film formation upon the substrate surface. Still another problem is that the electrical components formed on the substrate may suffer charging damage due to a non-uniform plasma density.
Therefore, the inventors have provided an improved method and apparatus for controlling a magnetic field in a semiconductor wafer processing chamber.